Fix #518, provide --enforce-all option to check_added_large_files

The --enforce-all option when provided ensures that all files passed
on the command line are checked against the size limit.  Default
behaviour remains unchanged.

pre_commit_hooks/check_added_large_files.py

@@ -21,11 +21,20 @@ def lfs_files() -> Set[str]:
     return set(json.loads(lfs_ret)['files'])
 
 
-def find_large_added_files(filenames: Sequence[str], maxkb: int) -> int:
+def find_large_added_files(
+        filenames: Sequence[str],
+        maxkb: int,
+        *,
+        enforce_all: bool = False,
+) -> int:
     # Find all added files that are also in the list of files pre-commit tells
     # us about
     retv = 0
-    for filename in (added_files() & set(filenames)) - lfs_files():
+    filenames_filtered = set(filenames) - lfs_files()
+    if not enforce_all:
+        filenames_filtered &= added_files()
+
+    for filename in filenames_filtered:
         kb = int(math.ceil(os.stat(filename).st_size / 1024))
         if kb > maxkb:
             print(f'{filename} ({kb} KB) exceeds {maxkb} KB.')
@@ -40,13 +49,21 @@ def main(argv: Optional[Sequence[str]] = None) -> int:
         'filenames', nargs='*',
         help='Filenames pre-commit believes are changed.',
     )
+    parser.add_argument(
+        '--enforce-all', action='store_true',
+        help='Enforce all files are checked, not just staged files.',
+    )
     parser.add_argument(
         '--maxkb', type=int, default=500,
         help='Maxmimum allowable KB for added files',
     )
-
     args = parser.parse_args(argv)
-    return find_large_added_files(args.filenames, args.maxkb)
+
+    return find_large_added_files(
+        args.filenames,
+        args.maxkb,
+        enforce_all=args.enforce_all,
+    )
 
 
 if __name__ == '__main__':